U.S. field crop production is valued at more than $50 billion annually. Crops are known to be sensitive to air pollution stress. Even a small percentage reduction in crop yield due to air pollution exposure could cause billions of dollars in direct and secondary economic losses. The National Crop Loss Assessment Network (NCLAN) consists of a group of cooperating government and nongovernment organizations engaged in field work, crop modeling, and economic studies to assess immediate and long-term economic consequences of the effects of air pollution on crop production. The program will define the relationships between yields of major agricultural crops and doses of ozone, sulfur dioxide, nitrogen dioxide, and their mixtures using state-of-the-art technology in the field with realistic pollutant exposure regimes. These data will be used to assess the economic consequences of exposure of agricultural crops to these pollutants.